The invention relates to a press-in pin for an electrical press-in connection between an electronic component and a substrate plate with an electrical contact hole.
A press-in zone of such a press-in pin is usually covered with a tin layer which forms a low-resistance metallic contact when pressed into a metalized contact hole of the substrate plate. Lead-free tin alloys comprising a tin content of over 90 wt % tend to relieve mechanical stresses by the transport of ions while forming thread-like monocrystalline whiskers. This entails the risk that the thread-like monocrystalline whiskers that are several millimeters long cause short circuits on the substrate plate, in particular between adjacent contact regions, which short circuits cannot be tolerated by electronic components such as ABS or ESP circuits in motor vehicles. On account of considerations regarding recycling and environmental protection, the tin-lead alloys in tin coatings of a press-in pin, which prevent whiskers from forming, are however also not tolerable, in particular in the case of motor vehicle components which are increasingly intended to be recycled.
A method for protecting tin layers from whisker formation is disclosed by the German patent publication DE 1 093 097. In this method, a precious metal layer, preferably consisting of gold, is deposited on a practically pure, lead-free tin layer which was previously deposited. This not only has the disadvantage of an additional, complicated and also expensive (due to the precious metal) further deposition step but can also lead to problems of solderability of the tin coating when the deposited layer is too thick. In particular in the known method, the production of a press-in pin connection, in which a 50 angstrom thick gold layer would have to be removed and rendered ineffective, is not of primary importance but rather a long shelf life of components comprising tin coated contact pins is intended to be achieved, said contact pins being intended to be soldered in a stress relieved manner when being mounted to the substrate plates in a stress relieved manner. A press-in pin is however intended to save exactly this step of fusion soldering to a substrate plate.
Furthermore, the Japanese patent specification JP 2005 25 20 64 A discloses a connecting piece for flexible printed circuit boards or flexible flat cables and plugs, wherein whiskers can be prevented from forming in the case of said connecting pieces by liquid resin being injected around a friction-welded connection between the contact surface of the printed circuit board and the flat cable terminal planarly applied to said connecting piece. The resin is intended to protect the planar connecting region between the copper connection of the substrate and the tin coating of the flat cable applied to said connecting piece. In the case of this disclosed connecting piece, the whisker formation on tin coatings is prevented by a subsequent resin coating of the copper-tin connection; however, a whisker formation is not thereby prevented after the tin coated press-in pin of an electronic component has been pressed into a contact hole of a substrate plate.